All-electric measurement of spin texture used for spin current generation will contribute to easier and cheaper way of developing spintronic devices
The magneto-resistance effect is the tendency of a material to change the value of its electrical resistance in an externally-applied magnetic field. It has been widely utilised for applications in sensors and hard disk reading heads.
Figure: (a) Schematic diagram illustrating the Dirac cone of a topological insulator. (b) Spin-momentum locked surface state with hexagonal warping. (c,d) Hall bar device of topological insulator Bi2Se3 for harmonic resistance measurements. (e) Second harmonic resistance signal for the three scans of magnetic fields in xy, zy, and zx planes.
Credit: National University of Singapore
So far, no link has been established between the existing magneto-resistances and spin texture of spin-polarised materials. Researchers from the National University of Singapore (NUS) have recently made a breakthrough in this field, revealing a close relation between the spin texture of topological surface states (TSS) and a new kind of magneto-resistance.
This fundamental advancement is achieved in collaboration with researchers from the University of Missouri, United States. The research team observed for the first time a novel magneto-resistance in three-dimensional (3D) topological insulators (TIs), which scales linearly with both the applied electric and magnetic fields, and shows a close link to the in-plane and out-of-plane spin textures of TSS. The team's finding could help in addressing the issue of spin current source selection often faced in the development of spintronic devices.
The research team, led by Associate Professor Yang Hyunsoo from the Department of Electrical and Computer Engineering at the NUS Faculty of Engineering, published their findings in the journal Nature Physics.
New magneto-resistance found in 3D TI
The discovery of 3D TIs has generated great interest among international researchers to understand the physical properties of this new state of matter, and exploring its applications in optoelectronics and spintronics. So far, the magneto-resistances found in 3D TIs is current-independent, reflecting a linear response of the electron transport to an applied electric field. At the same time, a transport obstacle exists in detecting the surface properties, due to the significant bulk contribution, which overwhelms the surface responses.
"In this work, we observed the second order nonlinear magneto-resistance in a prototypical 3D TI Bi2Se3 films, and showed that it is sensitive to TSS. In contrast with conventional magneto-resistances, this new magneto-resistance shows a linear dependence on both the applied electric and magnetic fields," said Dr He Pan, who is the first author of the study and a Research Fellow at the Department.
Assoc Prof Yang added, "Theoretical calculations by our collaborators from the University of Missouri revealed that the bilinear magneto-electric resistance originates from the spin-momentum locked TSS with hexagonal warping. From the perspective of the microscopic origin, it is a fundamentally new process regarding the conversion of a nonlinear spin current into a charge current under the external magnetic field."
Novel technique to probe 3D spin texture
Probing the surface spin texture is of critical importance for the development of TI-based spintronic devices. However, the approach performed to date is highly restricted to sophisticated tools such as photoemission spectroscopy.
The novel magneto-electric resistance observed by the research team provides a new route to detect the 3D spin texture in TSS by a simple electric transport measurement without involving any additional ferromagnetic layers. The team's study also revealed the hexagonal warping effect in TSS, which could previously only be determined by photoemission spectroscopy.
Commenting on the significance of the breakthrough, Dr He Pan said, "Our results can be applied to extended families of highly spin-polarised materials, like Rashba/Dresselhaus systems as well as two-dimensional transition metal dichalcogenides with spin-polarised states. It also provides a new route to detect the 3D spin texture of these materials by a simple transport measurement."
Moving forward, Assoc Prof Yang and his team are conducting experiments to increase the magnitude of the novel magneto-resistance by refining the TI materials and film thickness. They are also planning to incorporate and test the technology in different materials. The team hopes to work with industry partners to explore various applications with the novel magneto-resistance.
This research work was supported by A*STAR's Pharos Programme.
Goh Yu Chong | EurekAlert!
NASA's OSIRIS-REx mission explains Bennu's mysterious particle events
06.12.2019 | NASA/Goddard Space Flight Center
A momentous view on the birth of photoelectrons
06.12.2019 | ETH Zurich Department of Physics
University of Texas and MIT researchers create virtual UAVs that can predict vehicle health, enable autonomous decision-making
In the not too distant future, we can expect to see our skies filled with unmanned aerial vehicles (UAVs) delivering packages, maybe even people, from location...
With ultracold chemistry, researchers get a first look at exactly what happens during a chemical reaction
The coldest chemical reaction in the known universe took place in what appears to be a chaotic mess of lasers. The appearance deceives: Deep within that...
Abnormal scarring is a serious threat resulting in non-healing chronic wounds or fibrosis. Scars form when fibroblasts, a type of cell of connective tissue, reach wounded skin and deposit plugs of extracellular matrix. Until today, the question about the exact anatomical origin of these fibroblasts has not been answered. In order to find potential ways of influencing the scarring process, the team of Dr. Yuval Rinkevich, Group Leader for Regenerative Biology at the Institute of Lung Biology and Disease at Helmholtz Zentrum München, aimed to finally find an answer. As it was already known that all scars derive from a fibroblast lineage expressing the Engrailed-1 gene - a lineage not only present in skin, but also in fascia - the researchers intentionally tried to understand whether or not fascia might be the origin of fibroblasts.
Fibroblasts kit - ready to heal wounds
Research from a leading international expert on the health of the Great Lakes suggests that the growing intensity and scale of pollution from plastics poses serious risks to human health and will continue to have profound consequences on the ecosystem.
In an article published this month in the Journal of Waste Resources and Recycling, Gail Krantzberg, a professor in the Booth School of Engineering Practice...
03.12.2019 | Event News
15.11.2019 | Event News
15.11.2019 | Event News
06.12.2019 | Ecology, The Environment and Conservation
06.12.2019 | Life Sciences
06.12.2019 | Medical Engineering